Kaiser Effect in Sandstone in Polyaxial Compression with Multistage Rotation of an Assigned Stress Ellipsoid
- PDF / 475,067 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 170 Views
_____________________________ GEOMECHANICS _______________________________ ____________________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________
Kaiser Effect in Sandstone in Polyaxial Compression with Multistage Rotation of an Assigned Stress Ellipsoid I. A. Panteleeva*, V. A. Mubassarovaa, A. V. Zaitsevb**, N. I. Shevtsovc, Yu. F. Kovalenkoc, and V. I. Karevc*** a
Institute of Continuum Mechanics, Ural Branch, Russian Academy of Sciences, Perm, 614013 Russia *e-mail: [email protected] b Perm National Research Polytechnic University, Perm, 614990 Russia **e-mail: [email protected] c Ishlinsky Institute for Problems in Mechanics, Moscow, 119526 Russia ***e-mail: [email protected] Received May 22, 2020 Revised May 29, 2020 Accepted May 29, 2020
Abstract—The authors examine Kaiser effect in sandstone in nonproportional triaxial cyclic compression tests with stage rotation of an assigned stress ellipsoid through an angle of 90°. The load program consists of three pairs of cycles such that the maximal nominal stress of the second cycle exceeds the first cycle stress by 20 MPa at the constant side support. Cyclic loading is applied to sandstone in three orthogonal directions, with two cycles in each direction. Kaiser effect only appears in the second loading in the same direction, and activation of acoustic emission upon the change in the active loading direction is independent of the earlier reached stress level. This fact points at the orientation-driven nature of Kaiser effect, which means the material remembers its lattermost internal damaged structure. Keywords: Kaiser effect, acoustic emission, true triaxial loading, assigned stress ellipsoid rotation, deformation memory effect, test system. DOI: 10.1134/S1062739120036653
INTRODUCTION
In the middle of the XX century, when conducting experiments on cyclic deformation of rocks, J. Kaiser discovered the memory effect—absence of acoustic emission pulses in the material under cyclic loading until the maximum load level of the previous cycle is reached [1]. The activity of acoustic emission increases abruptly upon reaching this level. A large number of studies aimed at studying the conditions for the Kaiser effect in rocks of different genesis and under different loading conditions have been currently conducted [2–12]. One of the important practical trends of using this effect is the development of methods for monitoring the stress-strain state of the rock mass, including artificial anisotropic materials [4, 13–22]. Experimental studies of rock deformation behavior under cyclic uniaxial compression with side support according to the Karman scheme showed that an abrupt jump in the acoustic emission activity in the second and subsequent cycles is observed when not the maximum level of applied axial stress is reached in the previous cycle, but the level of maximum differential stress Δσ = σ
Data Loading...
